Optical film

ABSTRACT

Optical films having anti-Moiré and anti-wetout features are described, along with systems and methods for making these optical films. A master used to make optical films is formed using a single axis actuator cutting along a trajectory that is out of plane with the surface of the master. Movement of the cutting tool along the trajectory cuts grooves having variable depth and variable pitch into the surface. Prisms formed from the master have variable depth, variable height prisms that provide anti-wetout and anti-Moiré features.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing under 35 U.S.C. 371 ofPCT/US2008/071122, filed on Jul. 25, 2008, which claims priority to U.S.Provisional Application No. 60/974,245, filed on Sep. 21, 2007, thedisclosure of which is incorporated by reference in its/their entiretyherein.

TECHNICAL FIELD

The present invention is related to optical films having anti-Moiré andanti-wetout features, and systems and methods for making optical filmswith anti-Moiré and anti-wetout features.

BACKGROUND

Optical films having prismatic structures are used to improve theappearance of displays. A display device may use several different typesof films to enhance display brightness by directing light from thedisplay light source along a preferred viewing angle.

Optical films increase desirable display characteristics such asbrightness and contrast, but can also introduce undesirablecharacteristics. For example, overlaying multiple optical films in adisplay may result observable defects caused by wetout and/or Moiréeffects.

There is a need for optical films that increase desirablecharacteristics of displays such as brightness and contrast whilereducing defects that are distracting to the viewer. The presentinvention fulfills these and other needs, and offers other advantagesover the prior art.

SUMMARY

Embodiments of the invention are directed to optical films havinganti-Moiré and anti-wetout features, and systems and methods for makingoptical films with anti-Moiré and anti-wetout features.

One embodiment of the invention is a system for modifying a surface toproduce a master for making optical films. The system includes a cuttingtool used to cut grooves into the surface of the master. A drivemechanism provides relative motion between the cutting tool and thesurface. A single axis actuator is coupled to move the cutting toolalong a trajectory that is out-of-plane with the surface. The trajectoryhas a non-zero x-component, perpendicular to the surface, and a non-zeroz-component, parallel to the surface. Movement of the cutting tool alongthe trajectory during the relative motion between the cutting tool andthe surface cuts grooves having variable depth and variable pitch intothe surface. In some configurations, the surface is cylindrical. Inthese configurations, the drive mechanism is configured to provide therelative motion between the cutting tool and the surface by rotating thecylindrical surface.

According to one aspect, the system includes a controller configured togenerate a signal to produce non-random, random, or pseudo-randommovement of the cutting tool.

The actuator may be a single axis piezoelectric actuator oriented withrespect to the surface so that a direction of operation of the actuatoris along the trajectory. The trajectory may have an angle in a range ofabout 1 degree to about 89 degrees or in a range of about 91 degrees toabout 179 degrees relative to the plane of the surface. The variation inpitch and/or variation in depth can be in a range of about 0.5 micronsto about 50 microns with a wavelength of about 5 microns to about 500microns. The x and z components of the trajectory may be adjustable toachieve a desired amount of anti-wetout and anti-Moiré features in thefilm.

The drive mechanism may be arranged to move the cutting tool to producea low frequency variation in groove pitch of about 0.5 microns to about50 microns with a wavelength of about 500,000 microns. In thisarrangement, the low frequency variation in pitch is superimposed on thevariation caused by the movement of the cutting tool along thetrajectory. Additionally or alternatively, the drive mechanism may bearranged to move the cutting tool to produce a low frequency variationin groove depth of about 0.5 microns to about 50 microns with awavelength of about 2,000,000 microns. The low frequency variation indepth is superimposed on the variation caused by the movement of thecutting tool along the trajectory.

According to one aspect of the invention, the system may include amechanism configured to orient the cutting tool tip geometry at an anglewith respect to the surface. For example, the cutting tool tip geometrymay be oriented substantially perpendicular to the surface. In oneconfiguration, a spacer is disposed between the actuator and the cuttingtool to provide the desired orientation.

Another embodiment of the invention involves a method of modifying asurface to produce a master for making optical films. As a cutting toolis moved across a surface, the cutting tool is also moved back and forthalong a trajectory that has a non-zero x component, perpendicular to thesurface, and a non-zero z-component, parallel to the surface. Themovement of the cutting tool relative to the surface cuts grooves havingvariable pitch and variable depth into the surface. In oneimplementation, the surface is cylindrical and moving the tool acrossthe surface includes thread cutting the grooves into the cylindricalsurface.

In some implementations, the cutting tool movement cuts low frequencyvariations in groove pitch and/or groove depth that are superimposed onthe variation produced by the movement of the cutting tool along thetrajectory.

A further embodiment of the invention is directed to a master for makingoptical films. The master includes a surface with grooves in thesurface. The grooves have varying pitch and varying depth. The variationin pitch has a range of about 0.5 microns to 50 microns with awavelength of about 5 microns to about 500 microns and the variation indepth has a range of about 0.5 microns to about 50 microns with awavelength of about 5 microns to about 500 microns. The variation inpitch is dependent on the variation in depth.

The variation in pitch and depth may be superimposed on one or both of arelatively lower frequency variation in pitch and a relatively lowerfrequency variation in depth.

Another embodiment of the invention is directed to a prismatic opticalfilm, Each of the prisms of the film have variation in pitch andvariation in height. The variation in pitch and the variation in heightis in the range of about 0.5 microns to about 50 microns with awavelength of about 5 microns to about 500 microns. The variation inpitch is dependent on the variation in height. The variation in pitchand height of the prisms may be superimposed on one or both of arelatively lower frequency variation in prism height and a relativelylower frequency variation in prism pitch.

In certain configurations, the prisms may be substantially linear and/orsubstantially parallel or the prisms may be intersecting. A first set ofprisms may be interleaved with a second set of prisms, the first sethaving nominally greater height than the second set of the prisms. Afirst set of prisms having nominally greater pitch may be interleavedwith a second set of prisms. For example, the interleaving may be 1 to 1or may be according to another pattern.

Another embodiment of the invention is directed to an optical film thatincludes a substantially flat surface and a second surface having anarray of prisms comprising a first group of prisms interleaved with asecond group. Each of the prisms of a first group are substantially thesame height and have variation in pitch in a range of about 0.5 micronsto about 50 microns with a wavelength of about 5 to about 50 microns.The second group of the prisms have relatively greater height than thefirst group of the prisms. The prisms may be interleaved in a one to onepattern or may be interleaved in any other pattern. The variation inpitch of the first group of prisms may be random, pseudorandom, or nonrandom. The second group of prisms may also have pitch and/or heightvariations.

A further embodiment of the invention is directed to a system formodifying a surface to produce a master for making optical films. Amachine drive mechanism is configured to provide relative motion betweena cutting tool and the surface. The machine drive mechanism is alsoconfigured to move the cutting tool perpendicular to the surface to cutgrooves in the surface having a low frequency variation in depth ofabout 0.5 microns to about 50 microns. The system includes an actuatorconfigured to move the cutting tool parallel to the surface to cut highfrequency pitch variation in the grooves. The high frequency pitchvariation has a range of about 0.5 microns to about 50 microns and awavelength of about 5 microns to about 500 microns. The pitch variationmaybe random, pseudorandom, or non-random.

Another embodiment of the invention involves a method of modifying asurface to form a master for making the optical films. A cutting tool ismoved with low frequency to cut grooves in the surface. The grooves arecut with a low frequency variation in depth in range of about 0.5microns to about 50 microns. The cutting tool is moved with highfrequency to cut pitch variation in the grooves. The high frequencyvariation in pitch has a range of 0.5 microns to 50 microns with awavelength of about 5 microns to about 500 microns. The high frequencyvariation in pitch may be random, pseudorandom, or non-random. Themaster may be used to form prisms on a film.

In another embodiment of the invention, a master for making an opticalfilm includes a surface having grooves in the surface. Each groove has ahigh frequency variation in pitch in a range of 0.5 microns to 50microns with a wavelength of about 5 to about 500 microns and a lowfrequency variation in depth in a range of 0.5 microns to 50 microns.

Another embodiment is directed to an optical film having a substantiallyflat surface and a second prismatic surface. The prisms of the secondsurface have prism peaks that lie in a plane substantially parallel tothe flat surface. Each prism of a first group of the prisms have a highfrequency variation in pitch in a range of about 0.5 microns to about 50microns with a wavelength of about 5 microns to about 500 microns. Eachprism of a second group of the prisms have a high frequency variation inheight in a range of 0.5 microns to 50 microns with a wavelength ofabout 5 microns to about 500 microns. According to one aspect, theprisms of the first group are interleaved with the prisms of the secondgroup, where the interleaving pattern may be one to one or anotherpattern.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a diamond turning machine system configured tomanufacture a master roll used for fabricating prism films havinganti-Moiré and anti-wetout features in accordance with embodiments ofthe invention;

FIG. 2 provides a top view of a portion of a tool mount assemblyconfigured to mount a cutting tool and dual single axis actuators to adiamond turning machine for producing a master roll;

FIG. 3A shows a portion of a tool mount configured to mount a cuttingtool and a single axis actuator to a diamond turning machine inaccordance with embodiments of the invention;

FIG. 3B illustrates the trajectory of the cutting tool in the X-Z planefor the single axis actuator arrangement as shown in FIG. 3A;

FIG. 3C illustrates a spacer mounted between the actuator and thecutting tool which is used to maintain the angle of the cutting tool tipsubstantially perpendicular to the surface of the master roll inaccordance with embodiments of the invention;

FIG. 3D illustrates a tool shank for mounting a cutting tool to maintainthe angle of the cutting tool tip substantially perpendicular to thesurface of the master roll in accordance with embodiments of theinvention;

FIG. 3E illustrates a cutting tool lapped to provide a cutting tool tipthat is substantially perpendicular to the surface of the master roll inaccordance with embodiments of the invention;

FIG. 4 is a flow diagram illustrating a method of cutting a master usedto fabricate anti-Moiré, anti-wetout prism films in accordance withembodiments of the invention;

FIG. 5 illustrates a system for fabricating a prism film havinganti-Moiré and anti-wetout features using the master roll in accordancewith embodiments of the invention;

FIGS. 6A and 6B are perspective and cross-sectional views, respectively,illustrating a prism film fabricated using a master roll having x andz-axis excursions formed by cutting along an out of plane trajectory inaccordance with embodiments of the invention;

FIG. 6C is a cross-sectional view of a prism film having only pitchvariations without height variations;

FIGS. 7A and 7B are perspective and cross-sectional views of a prismfilm having prisms with high frequency variations in pitch to provideanti-Moiré features where some prisms having greater nominal height thanneighboring prisms to provide anti-wetout features in accordance withembodiments of the invention;

FIG. 8 illustrates a prism having prisms with high frequency variationsin height to provide anti-wetout which are interleaved with prismshaving high frequency variations in pitch to provide anti-Moiré featuresin accordance with embodiments of the invention;

FIG. 9 illustrates a prism film having gradual variation in the nominalpitch of the prisms along with high frequency variations in prism heightand pitch in accordance with embodiments of the invention;

FIG. 10 shows an example of an apparatus using a film having ananti-wetout, anti-Moiré surface in accordance with embodiments of theinvention; and

FIGS. 11A-11B are scanning electron micrographs illustrating prism filmshaving substantially parallel prisms with variations in prism pitch andprism depth fabricated using a master formed by the trajectory cuttingprocess in accordance with embodiments of the invention; and

FIGS. 11C and 11D are scanning electron micrographs illustrating prismfilms with intersecting prisms having variations in prism pitch andprism depth fabricated using a master formed by the trajectory cuttingprocess in accordance with embodiments of the invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings forming a part hereof, and inwhich are shown by way of illustration, various embodiments by which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

The use of films for displays is well known. For example, in backlitdisplays, brightness enhancement films use a prismatic structure todirect light along the viewing axis, thus enhancing the brightness ofthe light perceived by the viewer. As another example, a backlitcomputer display screen may use a number of different films in order toproduce a screen with high contrast and high overall brightness, whilesimultaneously maintaining high, uniform brightness in certain selecteddirections and lower brightness in other directions. Such screens mayuse several types of films, including diffusing films in combinationwith a prismatic film or a lenticular film.

One problem with using films in a display is that the cosmeticrequirements for a display intended for close viewing, such as acomputer display, are very high. This is because such displays areviewed closely for long periods of time, and so even very small defectsmay be detected and cause distraction to the viewer. The elimination ofsuch defects can be costly in both inspection time and in materials.

Defects are manifested in several different ways. There are physicaldefects such as specks, lint, scratches, inclusions etc., and alsodefects that are optical phenomena. Among the most common opticalphenomena are “wet-out” and Newton's rings. “Wet-out” occurs when twosurfaces optically contact each other, thus effectively removing thechange in refractive index for light propagating from one film to thenext. This is particularly problematic for films that use a structuredsurface for their optical effect, since the refractive properties of thestructured surface are nullified. The effect of “wet-out” is to create amottled and varying appearance to the screen. Newton's rings are theresult of a slowly varying air gap between two films, as may be createdby a particle of dust between two films. Newton's rings may be formed intransmission or in reflection. The result of Newton's rings is that theviewer perceives a contour pattern on the screen that may bedistracting. Moiré effects are caused by optical interference patternsthat can appear when two or more films having linear prisms ofsubstantially equal pitch are overlaid. The defects described above givethe display a non-uniform, mottled, or uneven look that is undesirableand distracting to the viewer.

Several approaches have been followed to overcome the problem of defectsin multiple-film display assemblies. One is simply to accept a low yieldof acceptable display assemblies produced by the conventionalmanufacturing process. This is obviously unacceptable in a competitivemarket. A second approach is to adopt very clean and carefulmanufacturing procedures, and impose rigid quality control standards.While this may improve the yield, the cost of production is increased tocover the cost of clean facilities and inspection.

Another approach to reducing defects is to introduce a diffuser to thedisplay, either a surface diffuser or a bulk diffuser. Such diffusersmay mask many defects, and increase the manufacturing yield at lowadditional cost. However, the diffuser scatters light and decreases theon-axis brightness of light perceived by the viewer, thus reducing theperformance. There continues to be a need to reduce the occurrence ofdefects in displays, so that the manufacturing yield may be improvedwith little additional cost while, at the same time, maintainingperformance.

Embodiments of the invention are directed to prism films that reduce theoccurrence of observable defects in displays incorporating the films,and to methods and systems for making such films. The prism films formedaccording to the approaches described herein provide both anti-Moiré andanti-wetout features by varying the height and pitch of the prisms.Variation in the prism pitch reduces the appearance of Moiréinterference patterns. Variation in prism height reduces the occurrenceof wetout regions.

The prism films described herein are particularly useful in liquidcrystal displays and are also useful in various types of projectionscreens, including overhead and rear projections screens. Prism filmswith anti-Moiré and anti-wetout features in accordance with theconfigurations described herein produce a number of unexpected andfavorable results. For example, anti-wetout features occurring at themaximum excursion may be advantageously positioned equidistant to eachother, providing more uniform support for the films. The ability toreduce defects and Moiré contrast is retained because variation in prismpitch is retained in the retracted peaks.

In some embodiments, a single axis out of plane motion is used tosimultaneously form variations in peak and depth in prism master on asurface that was nominally in plane. Films fabricated from these mastershaving these features yield dramatic results in anti-wetout performance.

Masters used to manufacture prism films have prism features cut into thesurface of the master in negative relief. After fabrication of themaster, the master may be used to manufacture a prism film by embossing,extrusion, cast and cure, and/or other processes, for example.

Prism film masters are typically cylindrical rolls having grooves thatare the negative of the desired prism shapes. The grooves may be cutinto the master by diamond turning. The surface of the master istypically of hard copper, although other materials such as aluminum,nickel, steel, or plastics (e.g., acrylics) may also be used. A numberof concentric grooves may be cut around the circumference of the masterroll. The master roll may be machined by a technique known as threadcutting, in which a single, continuous cut is made in the roll while thediamond tool is moved in a direction parallel to the surface of therotating master roll, or plunge cutting where a plurality of concentricgrooves are individually formed in the workpiece.

A diamond turning machine typically includes a controller that controlsthe movement of a cutting tool used to cut grooves in the master. Thediamond turning machine may independently control the depth that thecutting tool penetrates into the master and the lateral motion of thetool along the surface of the master. Additionally, the diamond turningmachine may independently control the rotational speed of thecylindrical master.

A diamond turning system configured to manufacture a master roll usedfor manufacturing prism films is illustrated in FIG. 1. A cylindricalmaster 100 is rotated around an axis 102 by a drum drive 104. Although,in this example, the master 100 is shown in cylindrical form, inalternative configurations, the master can be planar. An anti-wetout,anti-Moiré surface pattern may be cut into the master 100 by cuttingplunge cutting concentric grooves or by thread cutting a shallow groove110 on the master 100, i.e. translating the cutting tool 108 in thez-direction while cutting into the surface of the master 100. Becausethe surface of the master 100 forms the complementary surface of thefilm, local minima on the master surface correspond to local maxima onthe film surface when the film is fabricated.

Typically, a controller 106 drives the cutting tool mount 109 laterallyin the z-direction to move the cutting tool 108 along the rotatingmaster 100 to make a continuous, threaded cut, or discontinuousconcentric cuts. The controller 106 controls the speed of the drum drive104 and may monitor the angular position, Ψ, of the master 100.

The controller 106 controls the movement of the cutting tool mount 109to produce low frequency excursions of the cutting tool in thez-direction, parallel to the master surface, and to produce lowfrequency excursions of the cutting tool in the x-direction, normal tothe surface of the master. The controller 106 may also control themovement of the cutting tool 108 via one or more fast servo actuators138 to produce high frequency excursions of the cutting tool. The angle,θ, between the cutting tool 108 and the master surface 100 can also becontrolled. The size and shape of the cutting tool 108 are selecteddepending on the particular type of film that the master 100 is to beused to manufacture.

Movement of the one or more actuators 138 are used to produce short,fast excursions of the cutting tool 108, while movement of the cuttingtool mount 109 is used to produce longer, slower excursions of thecutting tool 108. The low frequency motion of the mount may be used tovary the surface cut in the master 100 by an amount greater than thestroke length of the fast servo actuators 138. The controller 106generates control signals that control the high and low frequencymovements of the cutting tool 108. The control signals may include a lowfrequency component directed to the cutting tool mount 109 and a highfrequency component directed to the actuators 138.

The high and/or low frequency components of the control signal may besynchronous to the rotation of the master 100 and may be a periodic,random, non-random, or pseudo-random. For example, movement of the oneor more actuators 138 may be controlled to make small, rapid movementsof the cutting tool 108 during movement of the mount 109 which iscontrolled to make larger, slower movements of the cutting tool 108. Assuch, the higher frequency movement of the cutting tool 108 produced bythe actuator 138 is superimposed on the lower frequency movement of thecutting tool 108 produced by the mount 109. The movement of the mount109 and/of the actuator 138 may be random, pseudo-random, or non-random.Pseudo-random movement may be achieved by computer generated randomness.It may be preferred to repeat the same random signal for each roll tool,such that they contain the same recorded randomness and the resultantstructure is same roll to roll. In some embodiments, the movement of theactuator 138 and/or tool mount 109 may be generally non-random, such asa periodic or sinusoidal pattern, which is randomized by a sporadicrandom movement that cause a phase shift in the pitch or depth patternof the grooves 110.

The one or more actuators 138 operate to move the cutting tool 108 athigh frequencies not normally obtainable by movement of the cutting toolmount 107. Each actuator 138 comprises a single axis fast tool servo,having a transducer, such as a piezoelectric transducer (PZT), or othertransducer for converting an electrical signal from the controller 106into movement of the actuator 138 which ultimately controls the motionof the cutting tool 108. The upper frequency limit of the fast servoactuator's response may lie in the range from several kilohertz to manytens of kilohertz, whereas the frequency response of the cutting toolmount is typically not greater than 5 Hz. For example, movement of thetool mount 109 may achieve a low frequency variation in groove pitch ofabout 0.5 microns to about 50 microns over a distance (wavelength) ofabout 500,000 microns. Movement of the tool mount 109 may achieve a lowfrequency variation in groove depth of about 0.5 microns to about 50microns with a wavelength of about 2,000,000 microns.

The length of the stroke that the actuator 138 produces may be, forexample, less than 50 microns, or in a range of about 0.5 micron toabout 50 microns with a wavelength of about 5 microns to about 500microns. This range of higher frequency variations may be employed toprovide enhanced defect-hiding and light scattering. In embodimentswhere a wide viewing angle is desirable, the finer pitch softens andsmoothens the cutoff angle of the display, for example. It will beappreciated that there may be a trade-off between length of stroke andupper frequency response.

The resulting grooves 110 cut on the surface of the master 100 have anaverage spacing between local x and/or z excursions around the rollcircumference that is dependent on the surface speed of the rollrelative to the cutting tool 108, and the average period of time betweenexcursions of the cutting tool 108. For example, a drum having adiameter of 12 inches may be rotated at 200 revolutions per minute,while actuator 138 drives a tool sinusoidally at about 20 Khz. Theresultant wavelength will be 160 microns in the plane of the actuationvector.

FIG. 2 provides a top view of a portion of a tool mount assembly 200that is used to mount a cutting tool 236 and actuators 218, 216 to adiamond turning machine. The tool mount assembly 200 includes a mainbody 212 capable holding a single axis x-direction actuator 218, asingle axis z-direction actuator 216, and the cutting tool 236. In thisexample, the actuators 216, 218 are PZT stacks. The PZT stacks 218, 216are arranged to move the cutting tool 236 in the x-direction andz-direction, respectively. The PZT stacks 218, 216 are securely mountedto the tool mount assembly 212 for the stability required for precisecontrolled movement of cutting tool 236. PZT stacks 218, 216 includeelectrical connections 230, 234 for receiving signals from thecontroller.

The cutting tool tip 235 may be oriented perpendicular to the surface ofthe master roll. Movement of cutting tool under control of the x-axisactuator 218 as the master rotates causes parallel grooves of variabledepth to be cut into the master. Movement of the cutting tool undercontrol of the z-direction actuator 216 as the master roll rotatescauses grooves of variable pitch to be cut into the master roll. In someconfigurations, the grooves may be substantially linear andsubstantially parallel at least for some distance. In some embodiments,the grooves may intersect.

A cutting tool assembly having independent x and z movements for use inmaking prism films is described in commonly owned U.S. PatentPublication 2007/0107568 which is incorporated herein by reference.

An embodiment of the invention is directed to systems and methods formaking a prism film master that uses only one single axial actuator tocontrol the movement of the cutting tool. The use of a single axisactuator may be used to cut grooves that have interdependent x and zcomponents.

The cutting tool is oriented with respect to the master so thatoperation of the single axis actuator causes the cutting tool to movealong a trajectory that has both an x-component and a z-component toproduce a cutting tool motion that is out of plane with the surface ofthe master. The out of plane movement of the cutting tool cuts groovesin the master roll that have variations in both groove depth and pitch.When the prism film is made using the master roll, the variable pitch,variable depth grooves in the master translate to variable pitch,variable height prisms. As previously discussed, the variable pitch,variable height prisms provide anti-Moiré and anti-wetout features inthe prism film.

The operation of one single axis actuator can produce a linear motion ofthe cutting tool to cut a groove having both depth and pitch variations.The use of a single axis actuator reduces the number of componentsneeded, simplifies the construction of the tool mount, simplifies thecontroller electronics, increases the speed at which the structuredfilms can be produced, and fabricates a master tool having bothanti-Moiré and anti-wetout prism features. The variation in pitchachievable using the single axis actuator is less than about 0.5 toabout 50 microns variation in pitch with a wavelength of about 5 toabout 500 microns. The variation in depth achievable using the singleaxis actuator is less than about 0.5 to about 50 microns variation indepth with a wavelength of about 5 to about 500 microns.

FIG. 3A shows a portion of a tool mount 300 configured to mount acutting tool 310 and a single axis actuator 320 to a diamond turningmachine. The cutting tool 310 and the actuator 320 are oriented so thatoperation of the actuator 320 (e.g., a PZT actuator) produces anoff-axis motion of the cutting tool 310. Operation of the PZT actuator320 moves the cutting tool 310 along a trajectory that has both x and zcomponents and is off axis with the surface of the master 325.

FIG. 3B illustrates the trajectory 350 of the cutting tool 310 in theX-Z plane for the single axis actuator arrangement as shown in FIG. 3A.The cutting tool 310 moves back and forth along the trajectory 350 tocut variable depth and variable pitch grooves in the master. Thetrajectory 350 can be tuned for a single axis actuator depending on theamount of x component and z component desired. The maximum hypotenuselength is dictated by the single axis actuator travel capability.

For example, a PZT stack capable of 20 microns of travel, the actuatorcould be rotated such that 3 microns of anti-wetout variation (x-axiscomponent) is desired. With the x axis component equal to 3 microns, andthe hypotenuse equal to 20 microns, then the actuator is oriented withrespect to the master surface at an angle, Γ, of 8.6 degrees. Using thePythagorean theorem, the anti-Moiré component along the z-axis iscalculated to be 19.7 microns.

The tip of the cutting tool 310 may be oriented perpendicular to thesurface of the master or may be oriented at an angle to the mastersurface. The tool tip orientation may be achieved many ways. Asillustrated in FIG. 3C, an orienting spacer 370 may be employed betweenthe PZT actuator 320 and tool shank 360. As illustrated in FIG. 3D, thetool shank 365 may include the desired geometry directly. The tool 310may be oriented on the shank 366 at the desired angle, as illustrated inFIG. 3A. The tool tip 305 may be lapped or formed to contain the desiredorientation as shown in FIG. 3E.

FIG. 4 is a flow diagram illustrating a method of cutting a master usedto fabricate anti-Moiré, anti-wetout prism films in accordance withembodiments of the invention. The cutting tool is moved 410 relative tothe surface of the master to cut grooves in the surface. The movement ofthe cutting tool relative to the surface may produce thread cutting of agroove in the surface of the master or cutting concentric grooves. Asthe cutting tool is moved relative to the surface, it is also moved 420via a single axis fast servo actuator back and forth along a trajectorythat has non-zero x and z components and is out-of-plane with thesurface. Movement of the cutting tool along the trajectory causes thegrooves cut in the surface to have both variable pitch and variabledepth.

A prism film having anti-Moiré and anti-wetout features may be formed bycasting between a pair of rollers that are spaced apart by a specificdimension, as illustrated in FIG. 5. In FIG. 5, a film 502 is pulledfrom a reservoir 501, through a die 500. The film 502 is nipped betweena nip roll 504 and a master roll 506 bearing grooves 507 that are thenegative of desired prism structures. The master roll 506 forms theprism pattern 508 onto the upper surface of the film 502. After passingbetween the rollers 504 and 506, the film 502 cools, for example, in acooler 520, and maintains the patterns embossed on it by the rollers 504and 506.

In one prism film embodiment, the master roll 506 bears grooves 507 cutby high frequency excursions of the cutting tool along a trajectory thathas non-zero x and z components that is out of plane with the surface ofthe master roll. The prisms formed by the master roll 506 may haverandom, pseudo-random, or non-random variations in pitch to provideanti-Moiré features and/or may have corresponding random, pseudo-random,or non-random variations in height to provide anti-wetout features. Forexample, the variation in prism height and pitch may have a range ofabout 0.5 microns to about 50 microns with a wavelength of about 500microns.

FIG. 6A illustrates a prism film 600 formed using a master roll having xand z-axis excursions formed by cutting along an out of planetrajectory. The lines depicted on the prism films of FIGS. 6A-6C areintended to more clearly illustrate height variations of the prisms. Theprism film 600 includes prisms 610 having both anti-Moiré variations inprism pitch, p, and anti-wetout variations in prism height, h. FIG. 6Bis a cross-sectional view of the prism peaks 610 of the prism film 600of FIG. 6A illustrating the variations in prism height and pitch. Forcomparison, FIG. 6C is a cross-sectional view of a prism film 650 havingprisms with only pitch variations without height variations.

In another prism film embodiment, the master roll bears grooves cut byhigh frequency motion of the cutting tool controlled by one single axisfast servo actuator coupled with low frequency x-axis motion of thecutting tool. The single axis actuator may be a z-axis actuator or asingle axis actuator providing out of plane x and z motion asillustrated in FIG. 3A. The prism film includes prisms having highfrequency variations in pitch to provide anti-Moiré features where someof the prisms have greater nominal height than neighboring prisms toprovide anti-wetout features. One example of this type of prism film isillustrated by the top and cross sectional views of FIGS. 7A and 7B,respectively. In FIG. 7A, prisms 701-708 exhibit variations in prismpitch. The nominal height of prisms 702 and 706 is greater than thenominal height of prisms 701, 703-705, 707, and 708. The lines depictedon the prism films of FIGS. 7A and 7B are intended to more clearlyillustrate height variations of the prisms.

In yet another prism film embodiment, the master roll bears a first setof grooves cut by high frequency z-axis motion of the cutting toolcontrolled by the z-axis actuator. The first set of grooves isinterleaved with second set of grooves cut by high frequency motion ofthe cutting tool controlled by the x-axis actuator. For example, themaster roll may have m grooves having z-axis variations interleaved withn grooves having x-axis variations. FIG. 8 illustrates a prism filmformed using such a master roll, where m and n=1. Prisms 801, 803, 805,807 have high frequency variations in height to provide anti-wetout. Theanti-wetout prisms 801, 803, 805, 807 are interleaved with prisms 802,804, 806, 808 having high frequency variations in pitch that provideanti-Moiré features.

In a further prism film embodiment, the grooves cut into the master rollinclude low frequency prism-to-prism pitch variations superimposed onhigh frequency pitch and depth variations formed by a single axisactuator providing cutting tool movement along a trajectory out of planewith the master roll surface. FIG. 9 illustrates a prism film 900 formedusing this type of master roll. The nominal pitch of the prisms 910varies gradually from prism to prism, such that the pitch, P₁, betweensome prisms is smaller than the pitch, P₂, between other prisms. Eachprism 910 also includes high frequency variations in height and pitchcorresponding to variations in pitch and depth cut by the fast motion ofthe cutting along the trajectory out of plane with the master surface asdiscussed above. Additional details regarding variable pitch prism filmsand method and systems for making such films is described in commonlyowned U.S. Pat. No. 5,919,551 which is incorporated herein by reference.

Films fabricated according to the present invention are preferably madeof a substantially transparent material. Bulk diffusion material may beincorporated in a film according to the invention, although in manycases this may degrade the performance of the optical film. In addition,multiple layers of film and material may be included in a single film inorder to produce a specific optical effect, such as a reflectivepolarization. Acrylics and polycarbonates are good candidates for filmmaterials. Also, the film may be a two-part construction where thestructured surface is cast and cured on a substrate. For example,ultraviolet cured acrylics cast on polyester substrates may be used.Films of polyethylene terphthalate (PET) have been shown to work well assubstrates on which structures may be cured. Polyethylene naphthalate(PEN) has also been shown to work well as a polymeric material formanufacturing optical films.

One example of an apparatus using a film having an anti-wetout,anti-Moiré surface is illustrated in an exploded view in FIG. 10. Aliquid crystal display (LCD) illumination module 1000 uses a fluorescentlamp 1002 and reflector 1003 as a light source to direct light into alight guide 1004. The light guide 1004 may have diffusely reflectingextraction dots 1006 on the lower surface 1007. A broadband, diffusereflector 1008 is positioned below the light guide 1004 to reflect anylight recycled from any components above the guide 1004. Light from thefluorescent lamp 1002 enters the side of the light guide 1004 and isguided along the light guide 1004 via internal reflection at thesurfaces of the guide 1004. A light ray 1010 incident on one of theextraction dots 1006 is diffusely reflected to produce a number ofdiffusive rays 1012.

Light propagating upwards from the extraction dots 1006 passes throughthe upper surface 1013 of the guide 1004. A diffuser 1014 may bepositioned above the light guide 1004 to further diffuse light extractedfrom the guide 1004, and thus make the subsequent illumination of an LCDdisplay 1024 more uniform.

Light continuing in an upwards direction may then pass through a upperand lower prism films 1018, 1016, each having a prismatic structure onan upper surface similar to the prismatic structures described herein.The films 1018, 1016 are arranged so that the prism axis of the upperfilm 1018 is oriented at an angle, such as about 90 degrees, withrespect to the prism axis of the lower film 1016. Light is recycled byeither the upper or lower prism films 1018, 1016 to be reflected by thereflector 1008. The pair of crossed films 1016, 1018 serves to directthe light output along a preferred viewing axis.

A reflective polarizing film 1020 is positioned above the upper film1018. The reflective polarizer 1020 transmits light of one polarizationand reflects light of an orthogonal polarization. Therefore, the lightpassing through the polarizing film 1020 is polarized. The lightreflected by the polarizing film 1020 may be recirculated by thereflector 1008.

An LCD matrix 1024 is positioned above the polarizing film 1020.Polarized light passing through the LCD matrix is spatially modulatedwith information, for example an image, which is then transmitted. Othercomponents may be included in the module 1000, such as a cover sheetbetween the upper film 1018 and the polarizing film 1020.

Backlit LCD displays as illustrated in FIG. 10 may be incorporated invarious devices, including televisions, computer monitors, portablegaming devices and cell phones, for example.

FIGS. 11A-11C provide micrographs of prism films formed in accordancewith the processes described herein. FIGS. 11A and 11B, respectively,illustrate top and cross sectional view of a prism film formed from amaster produced by the trajectory cutting process as described inconnection with FIGS. 3 and 4. FIGS. 11A and 11B show substantiallylinear, substantially parallel prisms with variations in height andpitch. FIG. 11C shows intersecting prisms formed by the trajectorycutting process. FIG. 11D shows another configuration of an intersectingprism film made by the trajectory cutting process.

Various configurations of films having prisms with anti-Moiré pitchvariations and anti-wetout height variations have been illustratedabove. It will be appreciated that the various prism structuresdescribed may be used in any combination to provide defect reducingfilms. For example, high frequency x and/or z variations may be used inany combination with low frequency x and/or z variations to provideprism films that provide anti-Moiré, anti-wetout films.

The foregoing description of the various embodiments of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be limited not by this detailed description, but rather by theclaims appended hereto.

What is claimed is:
 1. A system for modifying a surface to produce amaster for making optical films, the system comprising: a cutting tool;a drive mechanism configured to provide relative motion between thecutting tool and the surface; and a single axis actuator coupled to movethe cutting tool along a trajectory that is out-of-plane with thesurface, the trajectory having a non-zero x-component, perpendicular tothe surface, and a non-zero z-component, parallel to the surface,wherein movement of the cutting tool along the trajectory during therelative motion between the cutting tool and the surface is configuredto cut grooves having variable depth and variable pitch into thesurface.
 2. The system of claim 1, wherein: the surface is cylindrical;and the drive mechanism is configured to provide the relative motionbetween the cutting tool and the surface by rotating the cylindricalsurface.
 3. The system of claim 1, further comprising a controllerconfigured to generate a signal to produce non-random, random, orpseudo-random movement of the cutting tool.
 4. The system of claim 1,wherein the trajectory has an angle in a range of about 1 degree toabout 89 degrees or in a range of about 91 degrees to about 179 degreesrelative to the plane of the surface.
 5. The system of claim 1, whereinthe variation in pitch is about 0.5 microns to about 50 microns with awavelength of about 5 microns to about 500 microns.
 6. The system ofclaim 1, wherein the variation in depth is about 0.5 microns to about 50microns with a wavelength of about 5 microns to about 500 microns. 7.The system of claim 1, wherein the drive mechanism is configured to movethe cutting tool to produce a low frequency variation in groove pitch ofabout 0.5 microns to about 50 microns with a wavelength of about 500,000microns, the low frequency variation in pitch superimposed on thevariation caused by the movement of the cutting tool along thetrajectory.
 8. The system of claim 1, wherein the drive mechanism isconfigured to move the cutting tool to produce a low frequency variationin groove depth of about 0.5 microns to about 50 microns with awavelength of about 2,000,000 microns, the low frequency variation indepth superimposed on the variation caused by the movement of thecutting tool along the trajectory.
 9. The system of claim 1, wherein theactuator comprises one single axis piezoelectric actuator oriented withrespect to the surface so that a direction of operation of the actuatoris along the trajectory.
 10. The system of claim 1, wherein the x and zcomponents of the trajectory are adjustable.
 11. The system of claim 1,further comprising a mechanism configured to orient the cutting tool tipgeometry substantially perpendicular to the surface.
 12. The system ofclaim 11, wherein the mechanism comprises a spacer disposed between theactuator and the cutting tool.
 13. The system of claim 1, wherein thecutting tool is oriented at an angle, θ, with respect to the surface.